Primary biliary cirrhosis (PBC) is a liver specific autoimmune disease characterized by portal tract lymphocytic infiltration, selective destruction of biliary epithelial cells and antimitochondrial antibodies (AMAs). Our lab has been instrumental in advancing the study of PBC, work which began nearly 25 years ago with the identification and cloning of the mitochondrial autoantigens. However, a breakthrough in PBC requires an animal model and over the past several years our laboratory has described several such models. However, the model which recapitulates in greater similarity the features of human PBC, is a mouse transgenic for directed expression of a dominant negative form of TGF2 receptor type II (dnTGF2-RII) under the direction of the CD4 promoter. Using funds from an R21 award that led to the development of this model, we have reported that dnTGF2-RII mice develop AMAs of the identical specificity as humans, similar cytokine profiles in both sera and liver and have liver histology and immunohistochemistry similar to humans with PBC. Further, adoptive transfer of splenic dnTGF2-RII CD8+ T cells into B6 Rag1-/- mice transfers autoimmune cholangitis, whereas similar transfer of dnTGF-2RII CD4+ T cells transfers colitis. We propose to take advantage of these and other data, a logical extension of our R21 award to extensively dissect the immunopathogenic mechanisms that lead to biliary autoimmune disease. In particular, we propose three critical aims. Firstly, we have demonstrated that dnTGF2-RII CD8+ T cells are sufficient to transfer biliary pathology to Rag1-/- recipients and we propose to define the mechanism of dnTGF2-RII CD8+ T cell mediated disease using transfer and mixed bone marrow chimeric studies and an ontogenetic analysis of CD8+ T cells and an analysis of CD8+ T cell cytokine expression. Secondly, we will define whether dnTGF2-RII CD8+ T cell autoimmunity is antigen specific by taking advantage of our expertise in class I tetramer technology and by using dnTGF2-RII mice with a restricted TCR repertoire. Finally, we have recently published that deleting IL-12p40, but not IFN-3, in dnTGF2- RII mice prevents the development of disease. This is exciting in light of recent IL-12 polymorphism demonstrated in genome-wide association studies of human PBC. We will take advantage of our ability to produce unique murine constructs and we will dissect the cytokine mediated pathways that produce disease. We will backcross p35-/- mice (lack IL-12), p19-/- mice (lack IL-23), p35/19-/- mice (lack IL-12 and IL-23), p35/40- /- mice (lack IL-12, IL-23, and homodimeric IL-12p40), or p35/IL-17A-/- mice (lack IL-12 and IL-17A) mice to dnTGF-2RII mice. Furthermore, as sera IL-22 is significantly elevated in dnTGF-2RII mice, we will also backcross IL-22-/- mice onto dnTGF-2RII mice to further define the protective or inflammatory role of IL-22. We submit that use of our unique murine constructs and our rigorous dissection of the mechanism of autoimmune cholangitis in this model will provide important clues towards successful modulation of human PBC.